Web Services (WS) allow applications to share data, and to invoke capabilities from other applications without regard to how those applications were built, what operating system or platform they run on, and what devices are used to access them. Web Services are invoked over the Internet by means of industry-standard protocols including the Simple Object Access Protocol (SOAP); the eXtensible Markup Language (XML); and Universal Description, Discovery, and Integration (UDDI).
SOAP is an XML-based messaging technology standardized by the World Wide Web Consortium (W3C), which specifies the rules for locating Web services, integrating them into applications, and communicating between them. UDDI is a public registry where one can publish and inquire about Web services.
Web services security is also defined by standards. The Organization for the Advancement of Structured Information Standards (OASIS) has produced the SOAP message security standard. Part of the standard is the use of security tokens. These tokens are typically defined or referenced in the header of the SOAP message. The security tokens can be used for message authentication, digital signature and encryption/decryption. The specification defines a number of token types including User/Password pairs, X.509 certificates and Kerbos tickets.